Valveless generation of unidirectional flow was first experimentally proven by Gerhart Liebau in 1954 (“Uber ein ventilloses pumpprinzip”, Naturwissenschaften, 41,327, 1954). The effect is called the Liebau effect. However, such pumps are generally bulky, can only perform in a limited range of frequencies, are generally electromagnetically driven, and tend to have a high power consumption. For microfluidic flow systems, electroosmatic flow is often used. But it gives a very low flow rate.